Sealing technique for gas panel

ABSTRACT

In a method for sealing a gaseous display and/or memory device, an unfused, low-softening point glass rod sealant, arranged in a picture frame pattern, together with high-softening point glass spacing rods are positioned between a pair of aligned flat glass plates, and the resulting assembly is placed in an oven enclosure. The assembly is then heated above the softening point of the glass rod sealant which reflows and fuses the plates to establish a gas-filled envelope. As the sealing material softens, the upper plate settles u;on the spacing rods to thus establish a predetermined and uniform spacing within the envelope.

United States Patent Langston, Jr. et a1.

SEALING TECHNIQUE FOR GAS PANEL Inventors: Perry R. Langston, Jr.,

Poughkeepsie; Rao R. Tummala, Wappingers Falls; Donald M. Wilson,Kingston, all of N.Y.

173] International Business Machines Corporation, Armonk, NY.

Filed: Dec. 30, 1971 Appl. No.: 214,298

Assignee:

1 References Cited UNITED STATES PATENTS 3/1970 Baker et a1...v SIS/169R8/1967 Spiegler 29/630 B 10/1971 Willson 315/169RX Dec. 11, 19733,559,190 1/1971 Bitzer et a1 315/169 R X 3,602,756 8/1971 Bonnet313/1095 Primary Examiner-Charles W. Lanham Assistant Examiner-J. W.Davie Attorney-Joseph J. Connerton et a1.

[57] ABSTRACT In a method for sealing a gaseous display and/0r memorydevice, an unfused, low-softening point glass rod sealant, arranged in apicture frame pattern, together with high-softening point glass spacingrods are positioned between a pair of aligned flat glass plates, and theresulting assembly is placed in an oven enclosure. The assembly is thenheated above the softening point of the glass rod sealant which reflowsand fuses the plates to establish a gas-filled envelope. As the sealingmaterial softens, the upper plate settles u;on the spacing rods to thusestablish a predetermined and uniform spacing within the envelope.

6 Claims, 5 Drawing, Figures PAIEmmnmmazs 35,78,127

arm 1 0f 2 all FIG.1

FIG.5

1 SEALING TECHNIQUE FOR GAS PANEL CROSS-REFERENCE TO RELATEDAPPLICATIONS U. S. Pat. application Ser. No.2l4,l74 for Gas DisplayPanel Without Exhaust Tube Structure, by Donald M. Wilson, filed Dec.30, 1971.

U. S. Pat. application Ser. No. 214,348 for Gas Panel Fabrication," byP. H. Haberland et al., filed Dec. 30, 1971.

U. S. Pat. application Ser. No. 176,625 for Dielectric DischargeInsulator for Gaseous Discharge Device," by Peter H. Haberland et al.,filed Aug. EH, 1971.

BACKGROUND OF THE INVENTION A gaseous display and/or memory devicecomprises an open panel configuration of electrically isolated but notphysically isolated cells in which individual cells or sites areselected by energizing associated pairs of orthogonal drive linesdisposed on opposite sides of a gasfilled envelope which, whenappropriately and selectively energized, cause the gas in the sitesbetween the selected conductors to ionize. In order to providesubstantially uniform resolution over the entire display surface, it isessential that the space between opposing walls of the gas envelope bemaintained substantially uniform and that the walls of the chamber besealed to provide a gas-filled container. Ihitially, such panels weresealed using epoxy which produced outgassing, i.e., impurities in thegas mixture which substantially lowered the life of the panel. Onemethod for eliminating outgassing is bakeout of the panel in an oven,but the epoxy decomposed when subjected to a bakeout temperature ofapproximately 400C. In situ fabrica tion of gas panels utilized solderglass for sealing, but this presented a problem in obtaining a uniformdeposition of the solder glass sealant, resulting in an undesirablemanual operation in attempting to apply a uniform layer of solder glassto one of the panel plates. Finally, a sealing operation using transfertape was attempted, but this required an extra bakeout cycle to bakeoutthe binder and frequently resulted in entrapped bubbles producing aweakened seal.

SUMMARY OF THE INVENTION The foregoing problems are resolved and otherrelated objects achieved by arranging high-softening point glass spacingrods and low-softening point glass sealing rods in picture frameconfigurations between disjoint highsoftening point glass plates. In theheat fusion stage, the glass sealing material fuses the plates to form acontaining envelope around the gas surrounded by these elements. As thesealing material softens, the upper plate collapses gradually toward andsettles upon the spacing rods, the spacing rods having a diameter lessthan the initial thickness of the unfused sealant, establishing thepredetermined spacing of the plates and providing point-to-point contactaround the entire sealed surface. The glass sealant material is selectedto have viscosity sufficiently low to flow during the heat fusioncycling, and yet high enough so that it will not run off the voidsduring such cycling. Following the panel sealing, the panel is pumpeddown and backfilled during a bakeout operation to eliminate outgassingor other impurities, and the. tubular orifice projecting from one of theplates and utilized as a vehicle for evacnation and gas filling istipped off, thereby sealing the gas within the panel. Thus during thefabrication as described above, vacuum and gas are coupled to theenvelope while the exterior of the glass plates receives atmosphericpressure.

Accordingly, an object of the present invention is to provide animproved sealing method for a gaseous discharge device.

Another object of the present invention is to provide an improved gaspanel assembly utilizing soft glass sealant and hard glass spacing rods.

An associated object of the present invention is to provide an improvedprocess for providng a gas panel seal utilizing a soft glass rod sealantand a hard glass rod spacer wherein the upper plate settles upon thespacing rods during a bakeout operation thus establishing apredetermined and uniform spacing within the envelope.

The foregoing and other objects and features of the present inventionmay be more fully appreciated and understood by referring to thefollowing detailed description of a specific embodiment thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partially schematicperspective view of a gas panel constructed in accordance with theteaching of the instant invention.

FIGS. 24 are sectional views of the assembly of FIG. 1 before and afterthe heat fusion state of the assembly processing.

FIG. 5 is a schematic view of vacuum furnace apparatus utilized in thepractice of the present invention to provide evacuation, gas-filling andheat-sealing stages.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings and more particularly to FIG. 1 thereof, there is illustrated agaseous discharge assembly fabricated in accordance with the teaching ofthe instant invention. The panel assembly 1 consists of lower glasssubstrate 3 and an upper glass substrate 5 on which transversepassivated metallized conductor arrays 7 and 9, respectively, areformed. Conductor arrays 7 and 9 may be formed on substrates 3 and 5 bya number of well-known processes such as photoetching, vacuumdeposition, stencil screening, etc. While the conductor arrays 7 and 9may be wires or filaments of copper, gold, silver, aluminum or any otherconductive metal or material, formed in situ conductor arrays oftransparent, semi-transparent or opaque conductive material arepreferred since they are more easily deposited on and adhered to thesubstrates 3, 5. In the embodiment constructed in accordance with theteaching of the instant invention, opaque chrome-copper-chromeconductors having a split conductor configuration such as that describedin the foregoing application Ser. No. 214,348 are utilized in one of theconductor arrays as the preferred electrode configuration for maximumlight output. While not evident in FIG. 1 since they are transparent,each of the conductor arrays 7 and 9 have dielectric layers 11 and 13(FIG. 3) formed thereon. The two metallized passivated dielectric coatedfront and rear glass plates 3 and 5 and exhaust tube 15 are formed intoan integral structure by heat union of rod sealant 17 with dielectricplate coatings 11 and 13 of glass substrates 3 and 5, respectively. Thebroken-away portion of FIG. 1 indicates an edge spacer rod 23, one ofwhich would be utilized around each edge in the preferred embodimentshown in FIG. 1. However, the number, spacing and configurations of thespacing rods may vary with various considerations such as the geometryof the panel and are still considered to fall within the scope of theinstant invention. The fused seal is indicated in the broken-awaysection of FIG. 1 as element 25. The dielectric layers 11 and 13 (FIG.2), formed from sprayed and heated glass frit, cover the conductorarrays indicated schematically as 7 and 9 in FIG. 1 intersecting atilluminable crosspoints of the panel. All glasses used in thefabrication of the subject panel such as the substrate, dielectriclayers, orifice, orifice sealant, border sealant, etc., must havecompatible thermal coefficients of expansion, albeit differing optical,physical, dielectric and heat-softening properties. The glass substrates3 and 5 have substantial thickness (e.g. onefourth inch), the onlyrequirement for such support members being that they be nonconductiveand good insulators and substantially transparent for display purposes.Ordinary inch commerical grade soda-limesilica glass is utilized in thepreferred embodiment. While the panel illustrated in FIG. 1 isrepresentative of a panel after scaling in accordance with the instantinvention, reference is made to FIGS. 2-4 for a more completedescription of the operation of the sealing process.

Referring now to FIG. 2, the relative position of the glass plates 3 and5 with their associated dielectric coated conductor arrays prior to thesealing process is illustrated. While shown exaggerated for ease ofunderstanding, the relative size of sealing rod 17 with respect to thespacing rod 23 is illustrated. In a preferred embodiment constructed inaccordance with the instant invention, the soft glass sealant 17 isapproximately 40 mils in diameter, while the spacer rod 23 isapproximately 7 mils in diameter. However, as noted previously, theconfiguration of the rods may vary, and other configurations of bothsealing and spacing rods such as rectangular rods could be substitutedfor the circular rods illustrated in the preferred embodiment. When laidout in the general configuration shown in FIG. 2, the component parts ofthe panel are placed in an oven which is then heated to a temperaturesufficient to produce wetting or melting of the low-softening pointenvelope sealant 17 which, as previously described, comprises in thepreferred embodiment a single rod in the form of a picture framepositioned outside the normal display area of the panels. The peripheralspacer rod 23 could comprise a single rod in the same general pictureframe configuration or four or more separate spacer rods. The unjoinedassembly, when positioned in the desired orientation shown generally inFIG. 2, is placed in an oven enclosure and then heated in accordancewith the sequence more fully described hereinafter such that the softglass sealant 17 softens, flows and fuses with the dielectricmetallization coating layers 13 and 11. In practice, the sealing rodsare positioned beyond the viewing area of the panel and thus beyond theconductor configurations comprising conductor arrays 7 and 9, althoughthis is not a requirement. When the assembly reaches the wettingtemperature in the oven, the upper plate 5 gradually settles againstspacers 23, establishing the desired final dimensions of the gasfilledsealed envelope contained between the plates. While the weight of theupper plate 5 is normally adequate, a glass weight providing a pressureof up to 5 lbs. per square inch throughout the sealing area may be addedto upper plate 5. Thickness and viscosity of the unfused envelopesealant are selected so that upon softening and flowing the sealantforms a uniform void-free lining around the rectangular parallelepipedgas enclosure space shown within the sealed area bounded by seal 25 inFIG. 1. When the enclosure is returned to room temperature through acontrolled cycle, the fused border sealant hardens into a firm totallyimpervious seal. The resultant seal is shown in FIG. 3, wherein the rod17 has melted to the point shown as 17' and the space within the gasenvelope is controlled by the spacer rods 23. An enlarged view of theleft seal in FIG. 3 is illustrated in FIG. 4, and it will be appreciatedthat an identical sealing operation and sequence would simultaneouslytake place along the four edges to be sealed within the panel.

Referring briefly to FIG. 5, the apparatus for providing the pumpdown,bakeout and backfill operation re-' quired to fabricate a gas panel isillustrated schematically in FIG. 5. When the panel is sealed in themanner described above, the gas from a gas source 29 is applied throughconduit 31 and valve 33 to a metering valve 35 which controls the gas tothe desired pressure. Also connected to the metering valve 35 is anelectronic manometer 37, which is connected through conduit 39 to avacuum system. A mechanical pump comprising a portion of the vacuumsystem creates an initial vacuum below 50 TOR, while a diffusion pumpalso conventional creates a higher vacuum in the area of 10 to 10 TOR.After this pumpdown, a bakeout cycle is provided in oven enclosure 41 toeliminate any remaining impurities within the gas panel, and followingthe vacuum bakeout the panel is backfilled with gas from the gas source29. The apparatus of FIG. 1 is considered adequate for an understandingof the present invention. Typical parameters associated with thepreferred embodiment of the subject invention are as follows: Glassplates 3 and 5 are conventional soda-limesilicate glass one-fourth inchin thickness. The glass sealing rods 23 are a hard glass compositiondescribed more fully hereinafter which provide a uniform gas spacing of7 mils. Dielectric layers 11 and 13 may comprise 1 mil thicklead-borosilicate glass sprayed and fired at 600C. Metallizationconductors 7 and 9 are chrome-copper-chrome conductors having chromelayers of 1,000 angstroms and an intermediate copper layers of10,000-20,000 angstroms which are passivated in a forming gas asdescribed in the aforereferenced application Ser. No. 214,348. Thepreferred dielectric material has the following composition:

Lead Oxide PbO 74.46%

Boron Oxide B 0 14.95%

Silicon Oxide SiO 3.24%

Aluminum Oxide AI,O 7.35%

Summarizing the gas panel fabrication process utilized in the instantinvention, the plates, plate sealant, spacer tubes and tube sealants areprepared, the upper plate having a hole for tube coupling and theinterior surfaces of the plates metallized, i.e., having the metallicconductors deposited, etched and passivated and the lead-borosilicatepowdered glass frit which comprises the dielectric layer sprayed andreflown over the conductors. The component parts are then assembled inan unjoined state as shown in FIG. 2 and placed in the oven used onlyfor temperature cycling to heat-fuse the components into an integralassembly. When the panel has been sealed in the above described manner,

the space confined by the joint assembly is evacuated and baked out toestablish fusion of the tube sealant to the tube and outer surface ofthe rear plates and fusion of the soft rod sealant between the plates todielectric coating of the plates. Details of the specific duration andtemperature of the heating cycle are described in the aforereferencedcopending application Ser. No. 214,348. This and the other steps of theprocess are performed with the exterior of assembly at atmosphericpressure. The gas discharge device is checked for leaks and then coupledto the gas source as shown in FIG. 5 where the confined space in thepanel is filled with gas. The tube will then be tipped off or sealed,and the terminal connection processing completed. The terminalconnection processing comprises removing the dielectric and passivationcoatings from the plate metallization at appropriate edge terminationsites while the tests provided are the conventional tests applied to gasfilled envelopes and familiar to those skilled in the art. With respectto specific parameters of the preferred embodiment, the dielectriclayers 11 and 13 are 1 mil thick lead-borosilicate glass sprayed andfired at 600C, the metallization composition.chrome-copper-chrome havingupper and lower layers of chrome 1,000 angstroms in thickness and anintermediate layer of copper 10,000 angstroms thick. Passivation isprovided in forming gas with water vapor. In addition, the surfaces ofdielectrics l1 and 13 in contact with the gas may be formed from arefractory materialhaving a high secondary coefficient of emission asdescribed in the aforenoted copending application Ser. No. 176,625.

While the invention has been shown and described with reference to apreferred embodiment thereof, it will be understood that variousomissions, substitutions and changes in form and detail of the inventionas described herein may be made by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is theintention therefore to be limited only by the scope of the followingclaims.

What is claimed is:

l. A process for constructing a gaseous discharge display/storage devicecomprising assembling discrete parts, including transparent flat memberswith pre-processed printed circuit metallization and dielectric coating,a tubulation for exhausting and backfilling said gaseous dischargedisplay storage device, spacer rods and heat fusible sealing material,

said heat fusible sealing material being in the form of a sealing red,the cross-sectional area of said sealing rod being substantially largerthan the corresponding area of said spacer rods, and

heating said assembly of discrete parts to a temperature above thesoftening point of said sealing mate- III rial but below the softeningtemperature of said remaining components to effect fusion of saidsealing material and said transparent flat members into an impermeableenvelope confining a predetermined volume of gas whereby the spacebetween the walls of said envelope is controlled by the verticaldimension of said spacer rods.

2. The process according to claim 1 wherein said heat fusible sealingmaterial is of a greater viscosity than said spacer material to permitcontrol of the spacing between said transparent glass members by saidspacing means during the heating of said assembly of dis crete partsafter the softening temperature of said sealing material is reached.

3. The process according to claim 1 including the further step ofevacuating and backfilling said envelope through said tubulation with apredetermined volume of a gas at a pressure suitable for display usage.

4. A process for constructing a gas discharge display/storage devicecomprising the steps of arranging components, including transparent nonconductive plates with pre-processed printed circuit metallization anddielectric coating, a tubulation member, transparent spacer means andheat fusible sealing material in unfused condition, the cross-sectionalarea of said sealing means being substantially greater than that of saidtransparent spacer means,

placing said arranged components into an oven enclosure adapted forselective coupling to sources of vacuum, gas and heat,

cycling said oven to a temperaturee above the softening point of saidheat fusible sealing material but below the softening point of saidother components to effect reflow and fusion of said sealing materialand said transparent flat members into an impermeable envelope confininga predetermined volume of said gas,

evacuating said envelope and backfilling through said tubulation memberwith a predetermined volume of gas at a pressure suitable for displaypurposes, and

sealing the tube used for evacuating and backfilling of said displaydevice. 1

5. A process according to claim 4 wherein said transparent spacer meansand said sealing material are in the form of rods, the cross-sectionalarea of said spacer means controlling the distance between said flatplates during the reflow of said sealing material.

6. A process according to claim 5 including the further step ofweighting the upper plate to facilitate the settling of said upper plateon said spacing rods.

1. A process for constructing a gaseous discharge display/storage devicecomprising assembling discrete parts, including transparent flat memberswith pre-processed printed circuit metallization and dielectric coating,a tubulation for exhausting and backfilling said gaseous dischargedisplay storage device, spacer rods and heat fusible sealing material,said heat fusible sealing material being in the form of a sealing rod,the cross-sectional area of said sealing rod being substantially largerthan the corresponding area of said spacer rods, and heating saidassembly of discrete parts to a temperature above the softening point ofsaid sealing material but below the softening temperature of saidremaining components to effect fusion of said sealing material and saidtransparent flat members into an impermeable envelope confining apredetermined volume of gas whereby the space between the walls of saidenvelope is controlled by the vertical dimension of said spacer rods. 2.The process according to claim 1 wherein said heat fusible sealingmaterial is of a greater viscosity than said spacer material to permitcontrol of the spacing between said transparent glass members by saidspacing means during the heating of said assembly of discrete partsafter the softening temperature of said sealing material is reached. 3.The process according to claim 1 including the further step ofevacuating and backfilling said envelope through said tubulation with apredetermined volume of a gas at a pressure suitable for display usage.4. A process for constructing a gas discharge display/storage devicecomprising the steps of arranging components, including transparentnon-conductive plates with pre-processed printed circuit metallizationand dielectric coating, a tubulation member, transparent spacer meansand heat fusible sealing material in unfused condition, thecross-sectional area of said sealing means being substantially greaterthan that of said transparent spacer means, placing said arrangedcomponents into an oven enclosure adapted for selective coupling tosources of vacuum, gas and heat, cycling said oven to a temperatureeabove the softening point of said heat fusible sealing material butbelow the softening point of said other components to effect reflow andfusion of said sealing material and said transparent flat members intoan impermeable envelope confining a predetermined volume of said gas,evacuating said envelope and backfilling through said tubulation memberwith a predetermined volume of gas at a pressure suitaBle for displaypurposes, and sealing the tube used for evacuating and backfilling ofsaid display device.
 5. A process according to claim 4 wherein saidtransparent spacer means and said sealing material are in the form ofrods, the cross-sectional area of said spacer means controlling thedistance between said flat plates during the reflow of said sealingmaterial.
 6. A process according to claim 5 including the further stepof weighting the upper plate to facilitate the settling of said upperplate on said spacing rods.